U.S. patent number 4,141,356 [Application Number 05/852,760] was granted by the patent office on 1979-02-27 for respirator system and method.
This patent grant is currently assigned to Bourns, Inc.. Invention is credited to Paul R. Smargiassi.
United States Patent |
4,141,356 |
Smargiassi |
February 27, 1979 |
**Please see images for:
( Certificate of Correction ) ** |
Respirator system and method
Abstract
A respirator system with both assisted and spontaneous breathing
modes. A control circuit responds to the patient's breathing
pattern to alternate the system between the two modes in accordance
with a predetermined alternation pattern. The control circuit is
adjustable, enabling the frequency of assisted breaths to be
gradually reduced so that the patient can be weaned away from the
respirator and safely resume normal breathing under his own power.
The invention also includes the operating method contemplated for
such a system.
Inventors: |
Smargiassi; Paul R. (Riverside,
CA) |
Assignee: |
Bourns, Inc. (Riverside,
CA)
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Family
ID: |
24798099 |
Appl.
No.: |
05/852,760 |
Filed: |
November 18, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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696677 |
Jun 16, 1976 |
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Current U.S.
Class: |
128/204.23;
128/204.26 |
Current CPC
Class: |
A61M
16/00 (20130101); A61M 16/022 (20170801); A61M
2016/0024 (20130101) |
Current International
Class: |
A61M
16/00 (20060101); A61M 016/00 () |
Field of
Search: |
;128/145.8,145.6,145.5,142.2,188,DIG.17,DIG.29,2.08 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Recla; Henry J.
Attorney, Agent or Firm: Ware; Paul H. Becker; William
G.
Parent Case Text
This application is a continuation of application Ser. No. 696,677
filed June 16, 1976, now abandoned.
Claims
What is claimed is:
1. A respirator system comprising:
means for transmitting gas suitable for breathing to a patient;
means for supplying said gas to said means for transmitting;
means for sensing and producing an electronic signal indicative of
the patient's efforts to breathe;
means for counting and producing an electronic signal indicative of
a predetermined number of said efforts to breath made by the
patient;
electronic circuit means for determining and preselecting a desired
ratio of spontaneous breaths and producing an electronic signal
indicative thereof to assisted breaths to be furnished to the
patient;
first means for providing said gas to said means for supplying at a
pressure suitable for a spontaneous breath in response to said
patient's efforts to breathe;
second means for providing said gas to said means for supplying at
a pressure suitable for an assisted breath in response to said
signal produced by said means for determining and preselecting a
desired ratio of spontaneous breaths to assisted breaths to be
furnished to the patient; and
means for preventing the superposition of an assisted breath upon a
spontaneous breath.
2. The respirator system of claim 1, wherein said means for sensing
the patient's efforts to breath comprise:
means to maintain a constant reference pressure;
a constant reference pressure chamber maintained at said constant
reference pressure;
a first variable reference pressure chamber in first directional
fluid communication with said constant reference pressure
chamber;
an outlet port situate within said first variable reference
pressure chamber in fluid communication with the patient by means
of a conduit;
first flexible, resilient diaphragm means operable to open and
close said outlet port;
means for providing restrictive second directional fluid
communication between said constant reference pressure chamber and
said first variable reference pressure chamber;
assist transducer means in fluid communication with said constant
reference pressure chamber and with said first variable reference
pressure chamber for furnishing electronic signal responsive to
differential pressures therebetween;
second flexible, resilient diaphragm means situate in said assist
transducer means for responding to pressures in said constant
reference pressure chamber and pressures in said first variable
reference pressure chamber;
breath assist control circuit means responsive to said electronic
signal from said assist transducer means and developing an
electronic signal therefrom;
breath assist control switch means responsive to said electronic
signal from said control circuit means and developing a further
electronic output signal therefrom;
first piston means responsive to said further electronic output
signal and operative to charge a quantity of breatheable gas into
said means for supplying in response to said further electronic
output signal;
piston control means responsive to said electronic signal from said
breath assist control circuit means and developing another further
electronic output signal therefrom;
second piston means responsive to said another further electronic
output signal and operative to open and close said outlet port
situate within said first variable reference pressure chamber;
and
demand regulator means responsive to a patient's efforts to
breathe, and in fluid communication with said assist transducer
means and said constant reference pressure chamber.
3. The system of claim 2, wherein said second flexible resilient
diaphragm means separates a pressure applied from said constant
reference pressure chamber from a pressure applied from said first
variable reference pressure chamber.
4. The system of claim 3, wherein a pressure in said first variable
pressure chamber varies over a range from a reference pressure as
maintained in said constant reference pressure chambers, to less
than the reference pressure, in accordance with the patient's
efforts to breathe.
5. The system of claim 4, wherein a predetermined threshold
variation of pressure in said first variable reference pressure
chamber causes flexure of said second flexible resilient diaphragm
means so as to make an electrical contact.
6. The system of claim 5, wherein said predetermined threshold
variation of pressure in said first variable reference pressure
chamber is less than the variation of pressure in said pressure
sensing chamber sufficient to cause flexure of said third flexible
resilient diaphragm means.
7. The system of claim 2, wherein said demand regulator means
comprises:
a reference pressure chamber in fluid communication with said
constant reference pressure chamber;
third flexible, resilient diaphragm means forming one wall of said
reference pressure chamber;
a pressure sensing chamber having said third flexible, resilient
diaphragm means as a common wall between said pressure sensing
chamber and said reference pressure chamber;
an inlet chamber in fluid communication with said means for
supplying and having a central opening into said pressure sensing
chamber in a common dividing wall therebetween;
a rod connected between said third flexible, resilient diaphragm
means and a stopper operable to open and close said central opening
in response to mechanical movement of said third flexible,
resilient diaphragm means; and
check valve means to communicate a patient's inspiratory efforts to
said pressure sensing chamber while isolating expiratory pressures
therefrom.
8. The system of claim 7 wherein a pressure in said pressure
sensing chamber varies from a reference pressure as maintained in
said constant reference pressure chamber to less than the reference
pressure in accordance with the patient's efforts to breathe.
9. The system of claim 8, wherein a variation of pressure in said
pressure sensing chamber sufficient to cause flexure of said third
flexible resilient diaphragm means admits said gas suitable for
breathing to said inlet chamber and to said means for
transmitting.
10. The system of claim 9, wherein said breath assist control
circuit means comprises:
electronic logic means responsive to said means for sensing;
first one-shot circuit means responsive to said electronic logic
means;
means responsive to said first one-shot circuit means for counting
output signals furnished by said one-shot circuit means;
second one-shot circuit means responsive to and coupled to said
means for counting and furnishing its signal output to said breath
assist control switch.
11. The system of claim 10, wherein said means for counting
includes a plurality of integrally ordered output terminals, each
of which becomes energized in response to the same integrally
ordered number of output signals furnished by said one-shot circuit
means.
12. The system of claim 11, wherein said second one-shot circuit
means is coupled to said means for counting by means of a selector
switch adjustable by means of an adjustable contact arm to select
each of said plurality of integrally ordered output terminals so as
to select a desired ratio of spontaneous breaths to assisted
breaths.
13. The system of claim 12, wherein the adjustment of said selector
switch by means of said adjustable contact arm to one of said
plurality of integrally ordered output terminals thereby selects
the ratio of spontaneous breaths to assisted breaths defined by the
ordinal number of said one of said plurality of integrally ordered
output terminals as numerator to one as denominator.
14. The system of claim 1, wherein said means for counting and
producing an electronic signal indicative of a predetermined number
of said efforts to breathe made by the patient comprise:
electronic logic means responsive to said means for sensing and
producing an electronic signal indicative of the patient's efforts
to breathe;
first one-shot circuit means responsive to said electronic logic
means;
electronic counter means responsive to said first one-shot circuit
means responsive to said electronic logic means;
adjustable switch means receiving output signal from said
electronic counter means; and
second one-shot circuit means receiving the output signal from said
adjustable switch means.
15. The system of claim 14, wherein said electronic counter means
includes a plurality of integrally ordered output terminals, each
of which may be energized in response to the same integrally
ordered number of output signals from said first one-shot circuit
means.
16. The system of claim 15, wherein said plurality of integrally
ordered output terminals is coupled to said means for determining
and preselecting a desired ratio of spontaneous breaths to assisted
breaths.
17. The system of claim 16, wherein said means for determining and
preselecting a desired ratio of spontaneous breaths to assisted
breaths comprises:
a selector switch having an adjustable contact arm in adjustable
contact with said counter;
second one-shot circuit means responsive to output signal from said
electronic counter means having said adjustable contact arm of said
selector switch coupled to its input terminal.
18. The system of claim 17, wherein said adjustable contact arm is
adjustable over said plurality of integrally ordered output
terminals of said electronic counter means.
19. The system of claim 18, wherein said second one-shot circuit
means is effective to reset said electronic counter means in
response to signal generated therein as a result of preselection of
a desired ratio of spontaneous breaths to assisted breaths.
20. The system of claim 1, wherein said means for determining and
preselecting a desired ratio of spontaneous breaths and producing
an electronic signal indicative thereof to assisted breaths to be
furnished to the patient comprises:
electronic logic means responsive to said means for sensing and
producing an electronic signal indicative of the patient's efforts
to breathe;
first one-shot circuit means responsive to signal output from said
electronic logic means;
means responsive to said first one-shot circuit means for counting
output signals furnished by said first one-shot circuit means;
and
second one-shot circuit means responsive to and coupled to said
means for counting.
21. The system of claim 20, wherein said means for counting
includes a plurality of integrally ordered output terminals, each
of which becomes energized in response to the same integrally
ordered number of output signals furnished by said first one-shot
circuit means.
22. The system of claim 21, wherein said second one-shot circuit
means is coupled to said means for counting by means of a selector
switch adjustable by means of an adjustable contact arm to select
each of said plurality of integrally ordered output terminals so as
to select a desired ratio of spontaneous breaths to assisted
breaths.
23. The system of claim 22, wherein the adjustment of said selector
switch by means of said adjustable contact arm to one of said
plurality of integrally ordered output terminals thereby selects
the ratio of spontaneous breaths to assisted breaths defined by the
ordinal number of said one of said plurality of integrally ordered
output terminals as numerator to one as denominator.
24. The respirator system of claim 7, wherein said first means for
providing said gas comprises;
piston control means responsive to said means for sensing, for
controlling the position of a piston;
first flexible resilient diaphragm means responsive to the position
of said piston;
variable pressure chamber means in one-way fluid communication to a
constant pressure chamber and in fluid communication with an
expiratory branch having an outlet port within said variable
pressure chamber means which port may be opened or closed in
response to the position of said piston as controlled by said
piston control means;
bleeder conduit means between said variable pressure chamber means
and said constant pressure chamber permitting limited flow rate
from said constant pressure chamber to said variable pressure
chamber means; and
demand regulator means in fluid communication with said constant
pressure chamber.
25. The system of claim 24, wherein said demand regulator means
comprises:
a flexible resilient diaphragm that separates a constant reference
pressure chamber from a sensing chamber;
an inlet chamber in fluid communication with said means for supply
gas, said inlet chamber being separated from said sensing chamber
by a wall having a central opening;
a stopper situate in said inlet chamber, and attached to one end of
a rod whose other end extends through said central opening to said
flexible resilient diaphragm such that said stopper is driven by
the flexure of said diaphragm to open or close said central opening
and thus admit gas from said means for supplying to flow into said
inlet chamber;
means for transmitting said gas from said inlet chamber to a
patient.
26. The system of claim 25, wherein said means for transmitting
includes check valve means and means for filtering and humidifying
said gas.
27. The system of claim 1, wherein said second means for providing
gas comprises:
breath assist control switch means responsive to signal output from
control circuit means;
piston and cylinder means responsive to command signal from said
breath assist control switch means for containing a volume of said
gas when said piston is retracted from said cylinder and operable
upon said command to force said volume of gas into said means for
transmitting.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to medical respirators, and more
particularly to a respirator system and method having an
interruptable breath assist mode in which delivery of breathing gas
to a patient is initiated by the patient attempting to inhale.
2. Description of the Prior Art
Many respirators employ an "assist" mode to promote healthy patient
breathing in which the patient's breath activity is monitored and a
volume of air forced into his lungs when a breath attempt is
detected. The assisted breaths are generally provided at steady
rate until the patient is able to breathe on his own and it is safe
to disconnect the respirator. These systems are capable of
providing the patient with a sufficient amount of air to maintain a
safe oxygen supply for as long as he is unable to breathe under his
own power.
A problem may arise, however, in disconnecting the respirator. If
the patient is left on his own too soon, he will be unable to
breathe adequately and must be reconnected to the respirator
without delay. On the other hand, the respirator may be left in
place longer than is really necessary. In this case, in addition to
any discomfort to the patient or unavailability of the apparatus
for other patients that may be occasioned, the patient's return to
unassisted breathing, which is generally a gradual process in which
the patient builds up capacity breath by breath, may actually be
retarded.
An alternation between spontaneous (i.e., a patient initiated and
maintained positive pressure breath in which the patient controls
all the parameters such as tidal volume, pulmonary pressure, flow
rate, etc., except the blending of the breathing gases, i.e., the
fractional inspriatory oxygen concentration (FIO.sub.2), whereas on
the other hand, an assisted, sometimes referred to as simply as
assist breath, is one delivered to a patient in response to an
effort to breath put forth by a patient when he is too weak to
maintain the effort so as to obtain a full volume of air
unassisted. Thus, the ventilator in an assist mode controls all the
breathing parameters except the time of delivery of the breath. A
controlled, sometimes simply control, breath, in contrast to both
spontaneous and assist breaths, is one in which all breathing
parameters are controlled by the ventilator including the time of
delivery of the breath.) and assisted breathing has been achieved
in an existing system by providing a constant air stream from which
the patient can draw breaths upon demand, and superimposing thereon
an involuntary breath assist mechanism which forces a predetermined
amount of air into the patient's lungs at regular intervals
independent of the patient's spontaneous breathing. Such a system
may be adapted to wean a patient away from an assisted breathing
mode by gradually increasing the interval between forced breaths.
However, it is unresponsive to the patient's minute-by-minute
spontaneous breathing pattern, since an assisted breath is produced
at the preset time regardless of the spontaneous breathing rate. In
addition, there is a possibility of excess pressure being produced
when an assisted breath is produced on top of a spontaneous breath,
at which time the patient's lungs already contain an appreciable
amount of air.
Other systems have been used to interrupt a regular pattern of
assisted breaths, although not necessarily for the purpose of
weaning a patient from the respirator. For example, a binary
counter has been used to initiate a sigh (larger than normal air
volume) breath after a series of 32, 64, or 128 assisted breaths of
normal volume. While it has been found desirable to provide a
"sigh" control in the respirator system to periodically break the
constant breathing rate, such a mechanism does not contribute
towards reducing the patient's dependency on the respirator.
In another prior art device alternate spontaneous and assisted
breathing air conduits are provided. This respirator is normally
operated in the assist mode, but the spontaneous breath conduit
opens to override the assist mechanism if the patient begins to
breathe on his own before the time for the next assisted breath.
The device is most useful in the transition period when the patient
first begins spontaneous breathing, but is of more limited help in
the later stages of weaning a patient away from a respirator, since
breath assistance is provided only if the patient fails to breathe
spontaneously within a set time period.
SUMMARY OF THE INVENTION
In light of the above stated problems encountered in the prior art,
the general object of the present invention is to provide a novel
and improved respirator system and method for maintaining a safe
and regular supply of breathing air to a patient, while at the same
time being capable of gradually weaning the patient away from the
respirator until he has resumed full spontaneous breathing.
Another object of the invention is the provision of a novel and
improved respirator system and method for weaning a patient away
from the system in a manner responsive to the patient's individual
spontaneous breathing pattern, and yet provide adequate breathing
assistance for as long as required.
A further object of the invention is the provision of a novel and
improved respirator system having alternate spontaneous and
assisted breathing modes, in which the ratio of spontaneous to
assisted breathing can be adjusted to facilitate weaning of a
patient away from the system.
In the accomplishment of these and other objects, the present
invention provides a respirator system with both positive breath
assist means and means for providing breathing gas to a patient at
a pressure suitable for spontaneous breathing. A control circuit
actuates the breath assist means in a predetermined intermittent
manner in response to the breathing pattern obtained by a breath
attempt sensing means. The spontaneous breath supply means is
operably responsive to the combined presence of a sensed breath
attempt and nonactuation of the breath assist means, whereby
spontaneous breaths are supplied when the patient attempts to
breathe and an assisted breath has not already been provided.
According to one feature of the invention, the control circuit
includes resetable means to count the number of patient breath
attempts and actuate the breath assist means each time the breath
attempt count reaches a predetermined number. In this manner only
designated ones of the patient's breath attempts can trigger the
breath assist means, the remainder of the breaths being
spontaneous. Means are also included to adjust the breath attempt
count at which the breath assist means is actuated, thereby
enabling a patient to be gradually weaned away from the respirator
system by progressively increasing the interval between assisted
breaths until normal breathing is achieved.
According to another feature of the invention, a first pressure
sensing means senses the pressure in the breathing gas conduit
system and causes a control signal to be delivered to the control
circuit when the pressure falls below a first threshold level,
indicative of a patient attempt to breathe. The breath assist means
is actuated by the control circuit in response to the pattern of
received control signals. A demand regulator which includes a valve
means and a second pressure sensing means adapted to sense the
pressure in the conduit system controls the flow of spontaneous
breathing air, the demand regulator being adapted to open the valve
means and supply spontaneous breathing air to the patient when the
pressure sensed by the second sensing means falls below a second
threshold level which is less than the first threshold level
mentioned above. In a preferred embodiment, the first and second
pressure sensing means each compare the gas pressure in the conduit
system with a single reference pressure provided by a positively
maintained pressure plenum which is connected to the conduit system
by a bleeder means. Gas is conducted from the plenum to the conduit
system at a flow rate sufficient to compensate for normally
encountered gas leaks therefrom.
The invention also comprehends a novel and improved method of
operating a respirator system comprising the steps of sensing
patient attempts to breathe, selecting periodic nonconsecutive ones
of the sensed breath attempts, actuating a breath assist means in
response to each of the selected breath attempts, and actuating a
spontaneous breath supply means in response to the remainder of the
breath attempts. In a preferred embodiment of the method, the
sensed breath attempts are counted until a predetermined number is
reached, at which time the breath assist means is actuated and the
count is reset to an initial amount. A repetitive pattern of
alternation between assisted breaths and spontaneous breaths is
thereby produced, and by progressively increasing the interval
between assisted breaths the patient can be gradually and safely
weaned away from the respirator system.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages and features of the invention will be apparent
to those skilled in the art from the ensuing detailed description
thereof, taken together with the accompanying drawings, in
which:
FIG. 1 is a schematic diagram of a respirator system constructed in
accordance with the invention; and
FIG. 2 is a circuit diagram of a control circuit which governs
alternation between assisted and spontaneous breathing modes.
DETAILED DESCRIPTION OF A PARTICULAR EMBODIMENT
Referring to FIG. 1, an embodiment of the invention is shown in
which air and oxygen are respectively fed through a pair of
regulators 10 and 12 and delivered to a mixing valve 14 where the
gases are mixed to a proportion suitable for breathing by a patient
16. The air-oxygen mixture is fed from the mixing valve 14 to the
inlet chamber 15 of a demand regulator 18 which is further divided
into a reference chamber 20 and a sensing chamber 22, the last two
chambers being separated by a flexible, resilient diaphragm 24.
Inlet chamber 15 and sensing chamber 22 are separated by a wall 26
having a central opening 28 through which a rod 30 extends from the
diaphragm 24 to the interior of chamber 15. A stopper 32, affixed
to the end of rod 30 within chamber 15, normally abuts the dividing
wall 26 to cover opening 28, thereby preventing any flow of air
between chambers 15 and 22. This flow restriction is removed when
the gas pressure in chamber 22 is reduced by a predetermined amount
while the gas pressure in chamber 20 remains at a constant level.
In this event diaphragm 24 flexes into the area formerly occupied
by chamber 22 (to the right in FIG. 1), moving stopper 32 out of
contact with the dividing wall 26 and allowing gas to flow from air
and oxygen supplies through regulators 10 and 12, into and through
mixing valve 14 and through chamber 15 into chamber 22. The demand
regulator 18 thus functions much as a scuba tank regulator; a
pressure drop is produced when the user attempts to inhale, opening
up a line from an air supply.
Sensing chamber 22 is connected via a conduit 34 and check valve 36
to a breath assist mechanism denoted generally by the numeral 38.
The breath assist mechanism includes a piston 40 slidably lodged
within a cylinder 42. A control switch 44 governs the operation of
the breath assist mechanism. A negative pressure is created in
sensing chamber 22 when piston 40 is drawn backward (to the left in
FIG. 1), thus flexing the diaphragm 24 and thereby uncovering
opening 28 to enable an air flow from air and oxygen supplies
through regulators 10 and 12 into and through mixing valve 14,
through chamber 22, conduit 34, and check valve 36 into cylinder 42
as long as piston 40 continues to move backward. Breath assist
control switch 44 actuates the breath assist mechanism when
commanded by signaling piston 40 to drive forward, thus charging
the air mixture in cylinder 42 into the patient supply conduits 46
by way of check valve 49 and filter 50. The volume of gas delivered
to the patient may be either a preset amount, or determined
dynamically by providing well known apparatus to measure the
patient's lung pressure and terminate forward movement of piston 40
when the lung pressure reaches a desired level.
A plastic tubing network 46 provides a gas conduit between the
breath assist apparatus 38 and the patient 16. The conduit system
includes a check valve 48 which prevents a back flow of gas from
the patient to the breathing air sources, and a filter or
humidyfying device 50 to treat the breathing air before delivery to
the patient. An endotracheal tube 52 is fitted to the conduit
system in a T connection to conduct air to and from the patient
16.
The conduit system further includes an outlet or expiratory branch
54 having an outlet port 56 enclosed within a variable pressure
chamber 58, one wall of which forms a diaphragm 60 in registry with
outlet port 56. A piston 62 is located to alternately flex the
diaphragm 60 to a position blocking the outlet port 56 when the
piston is in a forward position, and to release the diaphragm 60
and allow gas to flow out of the conduit system 54 through outlet
port 56 when the piston 62 is in a retracted position. A piston
control device 64 such as a solenoid under the control of an assist
transducer 80 control circuit 90 causes the piston 62 to block the
outlet port 56 during inspiration and uncover the port during
expiration.
While the patient's breathing behavior may be sensed in a number of
ways, such as by measuring the pressure within the conduit system
46 and actuating the breath assist mechanism 38 whenever the
pressure falls below a particular level, in a preferred embodiment
the structure shown in FIG. 1 is employed. The chamber 58
communicates with a second chamber 66 through a check valve 68 that
permits a gas flow only from chamber 58 to chamber 66. The pressure
within chamber 66 is positively maintained at a constant level by
means of a gas jet source 70 that delivers a steady jet stream
through a venturi 72 and into the chamber 66. A number of outlet
orifices 74 are located between gas jet source 70 and venturi 72 to
allow gas exhaled by the patient to exit from the respirator
system. Gas jet source 70 is adjustable within a range that permits
the pressure inside chamber 66 to be set between zero and fifteen
centimeters H.sub.2 O gage (zero to approximate 0.2 pounds per
square inch gage). A bleeder conduit or line 76 enables a back flow
of gas from chamber 66 to enter chamber 58, with an adjustable
needle valve 78 forming a restriction in the line to limit the flow
rate (gas flows in the opposite direction, from chamber 58 to
chamber 66, are transmitted through check valve 68). Needle valve
78 may be adjusted from a full-open position, at which the gas flow
through bleeder line 76 is substantially unrestricted, to a
completely closed position.
Dynamic control of the breath assist mechanism 38 starts at a
pressure transducer 80 that is divided into two compartments by a
diaphragm 82, one compartment 59 being pressure-equalized with
chamber 58 by means of a connecting tube 84, and the other
compartment 61 equalizing in pressure with constant pressure
chamber 66 by means of a tap 86 from a second connecting tube 88.
The other end of tube 88 enters compartment 20 of demand regulator
18 to equalize the pressure therein with the constant pressure in
chamber 66.
It can thus be seen that the two compartments of pressure
transducer 80 are able to compare the variable gas pressure in
chamber 58 (which is equal to the pressure within the conduit
system 46 when the conduit outlet port 56 is uncovered) with the
constant pressure in chamber 66, the latter pressure being
positively maintained as a constant reference point. When the
pressure in chamber 66 exceeds that in chamber 58 by a
predetermined threshold amount, transducer diaphragm 82 flexes
sufficiently to make an electrical contact (not shown) and thereby
transmit a signal to a breath assist control circuit 90 over line
92. In the control circuit 90 the signal is processed in a manner
critical to the invention so as to actuate the breath assist
mechanism 38 in a predetermined intermittent manner. At the same
time, transducer 80 also transmits a signal to piston control 64
over line 91, causing piston 62 to move against the diaphragm 60
and block outlet port 56.
The trigger level of transducer 80 is adjustable within a suitable
range such as, for example, 0.05 centimeter H.sub.2 O to 1.0
centimeter H.sub.2 O, to permit the selection of a variety of
patient inspiratory efforts necessary to trigger the breath assist.
In any case the trigger level of transducer 80 is less than that of
demand regulator 18. The settings of needle valve 78 and transducer
80 are normaly determined by the expected voluntary inhalation flow
rate produced by the patient 16; gas flows through bleeder line 76
should be substantially unrestricted by needle valve 78 for flow
rates that are substantially less than the expected inhalation
rate. At such low flow rates the flow through bleeder line 76 is
sufficient to substantially equalize the pressures in chambers 58
and 66, thereby inhibiting transducer 80 from producing a control
signal. Larger back flows of gas are established from chamber 58 to
the patient through conduit branch 54 when the patient attempts to
draw a breath. When this occurs the flow of gas through bleeder
line 76 is restricted by needle valve 78 to a rate less than that
which is necessary to equalize the pressures in chambers 58 and 66,
thereby producing a pressure differential between the two chambers
that causes transducer 80 to trigger and produce a control signal
in response to a patient's effort to breath.
Referring to FIG. 2 for details of the control circuit 90, line 92
from the assist transducer 80 is connected to one input of a NOR
gate 94. A capacitor 103 is connected between NOR gate 94 and
one-shot circuit 96, which includes a pair of cross-coupled
inverters 98 and 100, a capacitor 102 connected in the first
cross-coupling branch between the output of inverter 98 and the
input to inverter 100, and a resistor 104 in the other
cross-coupling branch, is connected to the output of NOR gate 94 by
means of coupling capacitor 103. The output of the one-shot 96 is
delivered over line 106 to the counting input of a binary counter
108, and in addition is fed back to the other input of NOR gate 94
to ensure that capacitor 102 has sufficient time to charge when a
control signal is received from transducer 80.
The counter 108 is illustrated as having ten output stages 110,
numbered 0 through 9 in the drawing, although it should be
understood that the capacity of the counter is a matter of choice
and will be determined primarily by the maximum desired ratio of
spontaneous breaths to assisted breaths. A rotatable knob 112
(indicated in dashed-lines) carries a contact arm 114 that can be
set on any of the output terminals 110 of counter 108. Contact arm
114 is electrically connected through capacitor 116 to a second
one-shot 118, similar in design to one-shot 96, with inverters 120
and 122, a capacitor 124 in one cross-coupling branch, and a
resistor 126 in the other cross-coupling branch. One-shot 118
produces an output signal over an output line 128 to actuate breath
assist control switch 44 in response to an appropriate output
signal being produced by one-shot 118. Line 128 is also connected
to the reset input 130 of counter 108 such that the counter is
reset to its initial state each time it has counted up to the
output stage selected by switch arm 114.
In the embodiment shown, the signal at line 92 is normally at a
relatively low voltage or OFF state. Assist transducer 80 provides
an ON signal when a patient's attempt to breathe is sensed.
In operation, the described apparatus can be used to alternate the
respirator system between spontaneous and assisted breathing modes
in an efficient and controlled manner, such that the patient can
gradually be weaned away from the respirator as he regains his
breathing power. Selector switch 112 is initially set at the
particular counter output terminal 110 corresponding to the desired
ratio of spontaneous to assisted breaths. For example, if two
spontaneous breaths are desired for each assisted breath, contact
arm 114 is set at the "two" counter terminal, as illustrated in
FIG. 2. Different spontaneous to assisted breathing ratios may be
had by merely adjusting the selector switch 112 so that the contact
arm 114 connects with a different counter terminal.
Assuming the patient has just finished the end of an expiration and
is about to begin a new breath, piston 62 is in a withdrawn
position uncovering conduit outlet port 56, and the pressures in
chambers 58 and 66 are substantially equal. When the patient begins
to suck in at the beginning of the next breath, a partial vacuum is
created in chamber 58 that, because of the restriction imposed by
needle valve 78, can only partially be made up by a flow of air
through bleeder line 76 from chamber 66. The pressure imbalance
thus created between chambers 58 and 66 causes the diaphragm 82 of
assist transducer 80 to flex and establish an output signal. Piston
control 64 is thereby actuated to drive piston 62 forward into
diaphragm 60, blocking outlet port 56. At the same time a signal is
applied over line 92 to the control circuit 90, turning the input
to NOR gate 94 ON and its output OFF. This results in a change of
state of the succeeding inverters 98 and 100 and a charging of
capacitor 102, such that an output is produced over line 106 to
counter 108. Assuming the counter is initially reset, the applied
signal causes a positive output to be produced at the "zero" output
terminal 110. If selector switch 112 has been set to one of the
other counter output terminals as shown in FIG. 2, processing of
the signal through control circuit 90 is terminated at this point
and breath assist control switch 44 is left in an inactive state.
If, however, switch 112 has the setting as illustrated in FIG. 2,
that is, at counter terminal 2, the third such signal applied over
line 92 will be processed as heretofore described so as to cause a
signal to be applied by means of contact arm 114 through switch
112, and through coupling capacitor 116 to effect a change of state
in inverters 120 and 122, thus charging capacitor 124 such that an
output signal will be produced over line 128 so as to activate
breath assist control switch 44 and to reset counter 108. As the
patient continues to suck in air, a negative pressure is produced
in compartment 22 of demand regulator 18 which becomes great enough
to draw in diaphragm 24, moving stopper 32 away from opening 28 so
that breathing air can flow from mixing valve 14, through demand
regulator 18 and conduit system 46, to the patient, who now
completes the inspiration portion of a spontaneous breath. By the
time the patient is ready to exhale, the pressure within chamber 58
will have increased by air flow through bleeder line 76 to a level
at which transducer 80 permits piston 62 to retract. Outlet port 56
is thereby uncovered, allowing expired air to flow out of the
system through orifices 74.
Each succeeding attempt by the patient to breathe triggers assist
transducer 80 to advance the counting output of counter 108 by one
output state. Demand regulator 18 supplies breathing air for each
spontaneous breath until the counter output reaches the preselected
setting of switch 112. When this happens a triggering signal is
transmitted over contact arm 114 and through capacitor 116 to
one-shot 118. The resulting one-shot output over line 128 resets
counter 108 and completes an actuating circuit for breath assist
control switch 44. Actuation of switch 44 drives piston 40 into
cylinder 42, forcing the breathing air therein through the conduit
network 46 to the patient. In addition to providing the patient
with an assisted breath, the movement of piston 40 increases the
pressure within conduit system 46 to a level at which the
initiation of a spontaneous air flow from demand regulator 18 is
prevented. Piston 40 is thereafter withdrawn, creating a negative
pressure sufficient to draw a new supply of breathing air into
cylinder 42 from demand regulator 18, while check valve 48 isolates
the patient from the negative pressure.
It can thus be seen that the patient is allowed to breathe
spontaneously for a number of breaths equal to the particular
output 110 to which selector switch 112 is set, followed by an
assisted breath, the breathing air being efficiently supplied only
when required by the patient. Thereafter the pattern of the ratio
of spontaneous to assisted breaths is repeated for as long as the
selector switch 112 is left in place. If it is initially desired to
give the patient only assisted breaths, contact arm 114 is set on
the "zero" counter output terminal 110. Every succeeding attempt to
breathe is sensed by assist transducer 80, which causes counter 108
to produce an output at the "zero" terminal and thereby actuate
breath assist control switch 44. When the patient has recovered
sufficiently to breathe at least partially on his own, spontaneous
breaths may be introduced by setting selector switch 112 to a
higher order counter output. By gradually increasing the setting of
selector switch 112, the patient is allowed to breathe more and
more on his own and can be safely weaned away from the respirator
system while still retaining the benefit of occasional assisted
breaths. While theoretically counter 108 could have any number of
output stages, it is unlikely that more than about 20 would be
required. Within this range the breathing assistance rendered the
patient can be safely and conveniently controlled by the respirator
operator, who is able to make minute-by-minute adjustments based on
the patient's observed condition.
While a particular embodiment of the invention has been shown and
described, numerous additional modifications and variations are
possible in light of the above teachings. For example, an override
mechanism could be added to actuate the breath assist should the
patient fail to breathe within a predetermined time interval, or a
plurality of assisted breaths could be alternated with a single
spontaneous breath. It is therefore intended that the scope of the
invention be limited only in and by the terms of the appended
claims.
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